This invention relates to improvements in sealants used in making insulating windows for the building industry. Such windows are usually referred to as multiple glazed units. They are made by assembling two or more sheets, or panes of glass, spaced apart from one another by spacer elements around the edges which provides dead air space between the sheets of glass. To obtain optimum insulative effect, and to prevent air, water, vapors and dust from seeping into the dead air space, the sheets of glass must be hermetically sealed to each other and to the spacer elements. The spacer elements are usually made of metal. Also the multiple glazed units must be securely attached to a metal or wood frame by suitable sealant material.
One current practice in the insulating glass industry at the present time is to use a two part ambient temperature curing polysulfide sealant to assemble and seal the double or multipane glass units. This present practice is deficient in its ability to prevent the passage of moisture into the sealed unit because of the inherent relatively high moisture vapor transmission (MVT) of the polysulfide sealant. In attempts to overcome the deficiencies of the polysulfide sealant, for instance by incorporating plasticizers and chemical additives, other important properties such as resistance to ultraviolet radiation, adhesion, modulus and resistance to oils and plasticizers present in glazing compounds used in window installation, are adversely affected without improving the MVT of the polysulfide sealant to any appreciable extent.
Another practice in the industry is to use two sealants. An extruded butyl rubber tape sealant is applied as an innerseal to provide a good MVT resistant seal and then an exterior seal of a fast curing two part polysulfide sealant is applied to hold the glass panes in position. Butyl rubber alone is a non-curing sealant with good MVT resistance but it must be supplemented by a polysulfide sealant to provide quick setting to hold the panes together and the butyl rubber sealant, which provides good MVT resistance, can be allowed to set at its leisure. Thus dual sealant technology provides an acceptable product, but is objectionable because it is time consuming and costly.
Sealants based on dibrominated polybutadiene alone as the elastomeric constituent are known but are deficient in insulating glass sealants due to poor water resistance of the cured polymer and limited weather and ultraviolet light resistance. In addition the sealant is slow in attaining a tack-free surface after application.
Sealants based on low molecular weight butyl rubber alone as the elastomeric constituent are known but are deficient as insulating glass sealants because they are extremely slow in developing good tensile strength. They also require high levels of solvent in order to obtain a pumpable sealant. This results in a low solids sealant which when applied in an insulating glass unit results in an undesirable chemical fog between the panes.